Control apparatus



J 20, 1944- w. P. WILLS 2,352,143

CONTROL APPARATUS Filed April 27, 1940 2 Sheets-Sheet l INVEN TOR.

WALTER WILLS A TORNEY.

June 20, 1944. w. P. w|| s 2,352,143

C ONTROL APPARATUS Filed April 27, 1940 2 Sheets-Sheet 2 IN VEN TOR. WALTER P WILLS Patented June 20, 1944 CONTROL APPARATUS Walter P. Wills, Philadelphia, Pa., minor to The Brown Instrument Company, Pa, a corporation of Pennsylvania Philadelphia,

Application April 27, 1940, Serial No. 332,119

38 Claims.

The present invention relates to combustion control systems for fuel burners.

An object of the invention is to provide a combustion control system which operates in accordance with a characteristic of the fuel burner flame.

Another object of the invention is to provide a combustion control system embodying safety control provisions which operates in accordance with a characteristic of the fuel burner flame.

A further object of the invention is to provide a safety control system for a fuel burner which relies in its operation upon the characteristic fluctuating conductance of burner flames.

A still further object of the invention is to provide a safety control system for a fuel burner which employs a pair of electrodes in engagement with the burner flame and which is sensitive to the presence of a flame between the electrodes but is insensitive to other conductive paths therebetween.

A further object of the invention is to provide a control system for controlling the quality or extent of combustion in a fuel burner which relies in its operation upon the conductance between a pair of electrodes in engagement with the burner flame and otherwise insulated from I each other.

A stfll further object of the invention is to provide a control system for controlling the quality or extent of combustion in a fuel burner which a flame is not present is commonly employed to change the bias on the control grid of an electronic valve for controlling a thermal safety switch. Since there is a possibility that a low resistance path may be set up from the electrode to ground through other agencies than by means of the flame, for example, a low resistance path which may be established between the flame electrode and ground by reason of carbonization, by accidental touching of the electrode to ground, or by other abnormal conditions simulating combustion, provisions have been made in devices of the prior art for preventing the fuel supply and ignition from being turned on when such abnormal conditions exist. 1

Since an abnormal condition of this character simulating combustion may arise after the system is already in operation, it is desirable to provide means for distinguishing between such abnormal conditions and natural combustion while the system is in operation. For example, in a thermostatically controlled house heating system, if the control system is insensitive to the presence 0 the flame after initial ignition of the flame, the

fuel feeding means will be operated continuously as long as the room thermostat is closed. If the flame should then be extinguished, the furnace will be flooded with atomized fuel and a highly relies in its operation upon the characteristic fluctuating conductance of burner flames.

Another object of the invention is to provide a combined combustion quality and safety control system for a fuel burner which relies in its operation upon the conductance between a pair of electrodes in engagement with the burner flame and otherwise insulated from each other. A further object of the invention is to provide a combined combustion quality and safety control system for a fuel burner which relies in its operation upon the characteristic fluctuating conductance of burner flames.

In combustion control systems which have been proposed heretofore, various means have been employed for determining if combustion conditions are proper, and whether combustion actually takes place, one such means comprising an electrode which extends into the flame of the burner and which is so connected in the system as to provide a conductive path of relatively low resistance to ground through the flame. The variation in the'electrical conductivityof this path to ground when a flame is present and when explosive mixture of the latter will to accumulate.

Various means, independent of safety control meanshave been provided in the prior art for determining the quality of combustion in a bumer, that is for determining the degree of combustion of the fuel, and for controlling the mixture of fuel and air to the burner so as to secure optimum combustion conditions.

I have discovered that the conductance of a flame is not constant in magnitude, but is continuously fluctuating. In addition I have discovered that the amplitude of the fluctuations varies inversely with the degree of combustion of the burning fuel. That is to say, the amplitude of fluctuation of the flame conductance is larger be permitted when the flame is yellow, containing a large quana measure of the quality or degree of combustion of the burning fuel.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages andspecific objects obtained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

or the drawings:

Fig. 1 is a schematic diagram of a preferred embodiment of my safety combustion control system as applied to a fuel burner; and

Figures 2, 3, 4, and 6 show various modifications of the flame responsive circuit of my invention, which circuit may be used to operate either a safety control system or a combustion control system, or both.

Figure 1 of the drawings shows a gas burner I supplied with gas through conduit 2 and the flow of gas to the burner is controlled by an electrically operated or other suitable valve 3. A pilot burner 4 is provided which is controlled by an electrically operated or other suitable valve 5, and means are provided for igniting the pilot flame including a pair of electrodes 8 which are connected to the terminals of a secondary winding 1 of an ignition transformer 8 having a primary winding 9 which is adapted to be energized from the alternating current supply lines L and L.

The fuel valve operating circuit of my control system is controlled by means of a thermostat l8 which may be located in a room or space to be heated. The thermostat l8 may be of any suitable construction and includes a bimetallic element connected by means of conductor |2 to line L, and a contact blade l3 adapted to engage a stationary contact l4 which is connected to line L through a thermal switch I! and winding |8 of a transformer l1.

The thermal switch I5 is preferably of the,

form disclosed in the Patent 1,958,081, issued to F. S. Dennison, May 8, 1934. As shown more or less diagrammatically in the drawings, this switch comprises a stationary arm l8 and a movable arm |8 biased for movement away from arm I 8 but normally held in engagement with the latter by means of a bimetallic element 20. Element 28 is rigidly secured at one end to a block 2| and is arranged to be heated by a coil 22 when the latter is energized through a circuit which will later be described. Upon energization of coil 22 for a predetermined period of time, element 28 will be warped sufllciently in the clockwise direction to permit arm I! acting under spring or other bias to separate from switch arm |8 therebyinterrupting the circuit including thermostat Ill. The switch l8 will remain locked in this position until manually returned to its normal closed position.

Both the main burner and the pilot burner 4 are supplied with a'combustible mixture of fuel and air from the mixing chamber 23 into which fuel is introduced through conduit 24, and air through conduit 28. The amount of air passing through the conduit 28 is controlled by an electrically operated, or other suitable valve 28 which is adapted to be energized from the alternating current supply lines L and L The transformer H which supplies power for the control system comprises'the primary winding l8 and the secondary winding 21, having terminals 28 and 28 and a center tap 38. The portion of the secondary winding 21 between 8 terminal 28 and center tap 38 serves as a source of energy for an electric discharge device 3|, hereinafter referred to for convenience as the rectifier. The rectifier 3| may be of any suitable type, being shown in the drawings as a triode comprising an anode 32, a control electrode 33, a cathode 34, and a heater filament 38. Control electrode 33 is shown connected to cathode 34, so that the triode acts substantially as a diode. The rectifier 3| is adapted to charge a condenser 38, which is shunted by a resistance 38A, during the half-cycles when it is conductive, and the condenser 38 and resistance 38A are so proportioned that a substantial part of the charge is maintained on the condenser during alternate half-cycles, thus maintaining between its terminals a unidirectional potential, polarized as shown in the drawings. This charging circuit may be traced from center tap 38 of transformer secondary winding 21, through a conductor 31, condenser 38, and rectifler 3| to terminal 28 of the transformer winding. The center tap 38 is connected to ground as at 38.

The potential which is maintained by the con denser 38 supplies a circuit, hereinafter termed the detector output circuit, through a second electric discharge device 38, hereinafter referred to as the detector. The detector 38 is shown as a triode comprising an anode 48, a control electrode 4|, a cathode 42, and a heater filament 43. The detector output circuit may be traced from the positive terminal of condenser 38, through conductor 31, a resistor 44, anode 40, cathode 42, a cathode biasing resistor 45, and a conductor 48 to the negative terminal of condenser 38. 9 Control electrode 4| is connected through a condenser 41 and a conductor 48 to an electrode 48 which projects into the flame of the pilot burner 4. The conductor 48 is preferably encased within a shield 50, which is grounded, as at 8|. The control electrode 4| is also connected through a resistor 52 to the conductor 48. The conductor 48 is connected through a resistor 53 to the conductor 48. The difference of potential between the control electrode 4| and the cathode 42 is controlled by a circuit, hereinafter termed the detector input circuit, which may be traced from the positive terminal of condenser 38, through conductor 31, ground connection 38, a ground connection 84, pilot burner 4, the conductance, if any, existing between the burner and the flame electrode 49, the flame electrode, conductor 48, resistor 53 in parallel with condenser 41 and resistor 52, and conductor to the negative terminal of condenser 38. .As noted, the control electrode 4| is connected to the common terminal of condenser 41 and resistor 82.

When there .is a path of constant conductance between electrode 48 and burner 4, all the current traversing that path will pass through the resistor 53 because the condenser 41 will not pass direct current. There will, therefore, be no transfer of energy through the condenser 41 and accordingly the control electrode 4| will be at the same potential as conductor 48. Detector 38 will then be conductive. These conditions will obtain regardless of the value of the constant conductance, that is, regardless of whether it is RIO (absence of flame), of appreciable magnitude (grounded flame electrode'conditions) or some intermediate value.

when a flame existsbetween electrode 49 and burner 4, however, the current traversing. the flame will fluctuate in accordance with the varying conductance of the flame. This current'may be considered as composed of a constant direct component and a superimposed fluctuating component. The condenser 41 will pass the fluctuating component, and a fluctuating potential will thereby beproduced across the resistor 52. This fluctuating potential is applied to the control electrode 4| and operates to vary the flow of current in the output circuit of the detector'39 at the frequency of said fluctuating potential.

The potential difference established across the resistor 44 by the varying current flow in the detector output circuit is used to control a third electric discharge device 55, hereinafter referred to as the amplifier, and shown as a triode comprising an anode 55, a control electrode 51, a

cathode 58, and a heater filament 59. This control operation is effected. through the amplifier input circuit which may be traced from amplifier grid 51, conductor 50, resistor 44. through conductor 31 and cathode 55. The amplifier 55 is supplied with energy by that portion of the transformer secondary winding 21 between terminal 28 and center tap 38, and controls the flow of current through an output circuitwhich may be traced from terminal 28, through a conductor 5|, a relay winding 52 having a condenser 53 connected in parallel therewith, another relay winding 54 having a condenser 55 connected in parallel therewith, anode 55, cathode 58, and conductor 31 to center tap 38.

The relay winding 52 comprises a part of a relay 55, which also includes switch arms 51 and 58, cooperating with front contacts 59 and '10, respectively. The switch arm 58 is spring biased to engage with a back contact 1|. The term front contact is used to-indicate a contact on which a switch arm is closed when its associated relay winding is energized, and "back contact indicates one on which a switch arm is closed when its relay winding is de-energized. The relay winding 54 comprises a part of a relay 12, which also includes a switch arm 13, cooperating with a front contact 14 and a back contact 15. The switch arm 13 is biased to close on its back contact 15 by a spring 11 and is adapted to be moved against that bias force and against the opposing" force of a compression spring 19 into'engagement with contact 14. If the current flow through the relay winding 54 gradually increases from zero, it first overcomes the opposing bias of spring 11, and pulls arm 13 down until it engages spring 19. The spring 19 then balances the attraction of the relay winding and holds the switch arm 13 separated from both its front and back contacts. If the current flow through winding 54 continues to increase, it eventually becomes sufficient to overcome the opposing effect of both springs -11 and 19, and closes switch arm 13 on its front contact 14. By adjusting the tension on the spring 11 and the compression of spring 19, the current levels at which these two actions of relay 12 take place may be adjusted as desired.

As previouslyexplained, when a path of constant conductance exists between electrode 49 and burner 4, detector 39 is conductive. The potential difference across resistor 44 produced by this current makes control electrode 51 negative with respect to cathode 58, and maintains amplifier 55 substantially non-conductive. when a flame exists between electrode 49 and burner tial of cathode 58. It isnoted the frequency of the fluctuations of the flame conductance is greater than that of the current supplied by the transformer (the latter being of commercial frequency, for example, or 60 cycles). Thecondensers 53 and 55 are provided to smooth out the pulsating current which is passed by the amplifier 55, and thereby stabilizes the action of their associated relays. The relay 55 is designed to pick up its switch arm substantially as soon as the amplifier 55 becomes conductive. The relay 12 is designed to open the circuit through its back contact 15 when the current flow reaches a predetermined .level, and to close the circuit through its front contact 14 when thecurrent reaches a predetermined higher level, as explained previously herein.

When the temperature of the room or space to be controlled falls below the value it is desired to maintain, the thermostat Ill operates to move the switch blade l3 into engagement with the stationary contact l4, thus completing energizing circuits for the transformer primary l5, the ignition transformer primary 9, and the pilot burner valve 5. The energizing circuit for the ignition transformer primary 9 may be traced from line L through thermostat l8, thermal switch IS, a conductor 80, switch arm 58, backcontactJI, a conductor 8|, and winding gized from a separate secondary winding (not shown) on the transformer l1. Therefore, the valves 3|, 39 and 55, will be rendered operative after a short time delay required for the filaments to heat upon engagement of the thermo-.

stat contact arm l3 and contact l4.

The normal result of the opening of the pilot burner valve and the energization of the ignition transformer will be the appearance of a flame at the pilot burner. The presence of a flame at the pilot burner acts through the detector and amplifier circuits, as previously described, to energize relay winding 52, causing'switch arm 58 to close on front contact 10, and switch arm 51 to close on front contact 59. This de-energizes the ignition transformer 9 by opening its circuit at contact 1|, energizes the main burner valve 3, and shunts the heater coil 22 from the circuit of pilot burner valve 5. The energizing circuit for the valve 3 may be traced from line L through thermostat l8, thermal switch 5, conductor 88, switch arm 58, contact 18, a conductor 84, valve 3, and conductor 83 to line L The heater coil 22 is shunted through a conductor 85, contact 59, and switch arm 51. The

safety control system is then in full normal operation.

energized, the heater winding 22 of thermal switch II will remain energized, and will, after a predetermined time, open the switch I8 and thereby de-energize the entire system.

If the flame becomes extinguished after the system has attained full operation, the relaywinding 82 will be de-energized thus opening the circuit at contact I to the main burner valve 8 and thereby effecting closure of the latter, energizing the ignition transformer primary 8, and opening the shunt around heater winding 22. If a flame thereafter reappears, the system will again go into full operation, but if a flame'does not appear within a predetermined time, the thermal safety switch I 8 will operate to deenergize the entire system.

The air controlling. valve 28 is operated by a I reversible motor (not shown) which is energized for rotation in one direction through a circuit which may be traced from line L through conductor 88, switch arm l8, contact l5, conductor 81, valve 28 and conductors 88 and 83 to line L and is energized for rotation in the opposite direction through a circuit which may be traced from line L, conductor 88, switch arm 13, contact l4, conductor '88, valve 28, conductors 88 and 83 to line L. The motor is adapted to close the valve when it is energized through contact and conductor 81, and to open the valve when energized through contact 14 and conductor 88..

The valve 28 is provided with a limit switch (not shown) which operates to open conductor 81 and thereby deenergize the motor when the valve has been adjusted to its closed position. The limit switch is preferably so adjusted that the valve can never be completely closed. A second limit switch (not shown) is also provided for opening conductor 88 and thereby deenergizlng the motor when the valve 28 has been fully. opened.

When the system operation is first initiated, the switch arm 18 will be in the position shown, the valve 28 will be at its minimum opening, and the fuel mixture will accordingly be rich. This will result in the establishment of a yellow flame having a conductance which fluctuates widely, whereby the effective current value in the amplifler output circuit and thereby through relay winding 84 will be suflicient to' close the switch arm 13 against contact 14. This will-energize the motor of valve 28 in the direction to open the valve; As the valve opens, more air is supplied and accordingly, combustion becomes more complete. ,The amplitude Of the flame conductance variation decreases, and hence the current through relay winding 84 decreases, until it reaches a value at which springs Hand 18 bias switch arm 18 away from contact 14, but maintains it out of engagement with contact 18. The fuel mixture will then have its proper proportions, and the valve settin will remain constant until some change in fuel quality, for'example B. tau. content, or pressure, or the like, causes a change in the amplitude of flame conductance fluctuation outside the range for which. the de- In Fig. 21 have illustrated, more or less diagrammatically, a modified detector and amplifier circuit embodying my invention, in which the use of a separate rectifier is obviated by combiningin' a single triode the functions of the rectifier and detector. Fig. 2 also shows a modified relay system, in which a single relay 88A performs all the functions of relays 88 and 12 of Fig. 1. Parts in Fig. 2 which are the equivalents of correspond- 10. in; parts in Fig. 1 havebeen given the same Current pulses through this circuit during th half cycles when the anode is positive, and builds up a charge on condenser 38 such that its terminals have the polarity shown in the drawings.

The detector input circuit comprises the same elements as in Fig. 1, but functions in a slightly different manner, due to the fact that cathode 42 is connected to the positive terminal of condenser '88 rather than to the negative terminal. Theflame conductance in this circuit is in parallel with a circuit includingcondenser 4'! and resistor 52 in series, between one end of resistor 58 and the grounded positive terminal of condenser '88. When the conductance between the flame electrode 48 and the grounded burner is constant, thepotential across condenser 41 is also constant, and no current passes through it. Control electrode 4| of valve 88 remains, therefore, at substantially cathode potential. When a flame exists between electrode 48 and ground, however, its conductance varies, and a variable potential is impressed across condenser 41. A fluctuating current then fiows through the condenser, causing a. fluctuatin potential difference across resistor 52 and intermittently reducing the output of detector 38. The detector, therefore, responds to name conditions in the same way that the detector of the Fig. 1 arrangement responds to flame conditions.

The relay 88A in Fig. 2 operates all the switch arms for the combustion and safety control system of Fig. 1. Each switch arm and contact has been given the same reference numeral as in Fig. l, with the letter A added. The back contact 15A and the frontcontacts 88A and "A are mounted on springs 15B, 88B and 18B, respectively. y

When the average current flowing through relay winding 82A is below a certain level, for example, 10 milliamperes. the winding is not energized suificiently to lift its armature, and the switch arms are in the position shown in the drawings. As the current increases above 10 m. a., the winding is energized sufficiently to close switch arms 81A and 88A against contacts 88A and "A, respectively. Contact 15A, moved by compression spring 1513, follows switch arm "A and remains in engagement with it. If the current in winding 82A continues to increase beyond, say 20 m. a., the switch arms are moved further upward, as they appear in Fig. -2, compressing springs 88B and 10B and raising switch arm "A beyond the upper limit of movement of contact 15A and into engagement with spring 18A. Since there are now three prings, 88B, 18B, and 18A, opposing further upward motion of the armature, the current in relay winding 02A must increase still more, say, above 00 m. a., in order to bring switch arm "A into Went with contact 14A.

It may be seen, therefore, thatthe 01A and A have one of two alternative positions, dependent upon the relay current being greater or less than m. a.. in the siven example, and that the switch arm "A may take up any of three positions corresponding to the Illustrative relay currents ranges of 0-20, 20-90,

and over 30 m. a.. resp tiv ly. It should be apparentto thoseskilledintheartthattheaecurrent ranges may be limo to an desired value b adjusting the spr ns.

In Fig. 3 I have ill u strated another modification of the arrangement of Fig. 1 wherein safe positive with respect to the burner and to ground.

It is known that flame possess arectifying characteristic, that is to say, the conductivity of the flame is greater in the direction opposite to the direction of the flame propagation. The use of apositively biased flame electrode takes advantage of this characteristic. It is desirable to take advantage of this characteristic in that the position of the flame electrode in the path of the flame is less critical than when the flame electrode is negative in potential relatively to the burner as in the.1"igs. 1 and 2 arrangement. That is to say, the position of the flame electrode may then be adjusted considerably with respect to the flame without aifecting the circuit operation.

InFig.3Ihavealsoillustratedtheuseofa power amplifler whereby more positive operation of the relays 00 and I2 is obtained therebypermitting the use of heavier and more rugged relays.

The triode amplifler 00 of the. previous circuit tetrode 9| having an anode 92, a screen electrode 90, a control electrode 94, a cathode 90 and a heater filament 90. The amplifler output circuit may be traced from terminal 20 of the transformer secondary winding 21 through a conductor 9'I, relay winding 02 in parallel with condenser 03, relay winding 04 in parallel with condenser 90, anode 92, cathode 90, and a conductor 90 to tap "which in this circuit is closely adjacent terminal 29 of the secondary winding. The screen electrode 90 is connected through a resistor 99 to the conductor 91. The control electrode 94 is connected to the negative terminal of resistor 44 through a condenser I00, and to the terminal 29 of the transformer secondary winding 21 through a resistor III. The latter connectionis provided to bias the control electrode 94 negatively during the half cycles. of the sup.-

former secondary 21.

ularly desirable feature, especially, in the safety control system. as it would prevent operation of the system with a defective detector circuit.

In Fig. 4 I have illustrated a modification of the circuit arrangement of Fig. 8 in which the condenser 41 has been dispensed with and the functions thereof are performed by the condenser I00. Fig. 4 differs further from Fig. 3 in that a negative"flame electrode is employed. The

10 detector input circuit in Fig. 4 may be traced from the positive condenser 90 through conductor 01, ground 89, ground 04, pilot burner 4, the flame conductance, flame electrode 49 and resistances I02 and 52 in series to the negative terminal of condenser 36. Control electrode 4| is connected to the common terminal of resistor I02 and 02.

' when the conductance between electrode 49 and pilot burner 4 is constant, the potential of control electrode 4| and the output of detector 09 are also constant, and no current passes through condenser I00 to the control electrode 01 of amplifler 00. .When a flame exists between electrode 49 and burner 4, its varying conductance causes a like variation in the potential of control electrode 4| and in the output of detector 89, which is transmitted through condenser I00 to the control electrode 01 of amplifler 05. A condenser I03 is provided in shunt with the cathode biasing resistor 40 in Fig. 4 in order to stabilize the potential across that resistor when the detector output is fluctuating. The resistor I02 is provided to limit the flow of current between the control electrode 4| and cathode 42 upon the accidental occurrence of t e flame electrode 49 becoming grounded.

Fig. 5 illustrates a modified detector and amplifier circuit which employs a single electronic tube of the duplex-diode triode type, numbered I04 in the drawings, having an anode I05, a control electrode I06, and a cathode I01, two diode anodes I09 and I09 and a heater filament H0. The elements I00 and I 00 and I0! function as a triode and the diode anodes I09 and I09 cooperate with the cathode I0I.to form a half wave rectifier the circuit of which may be traced from arrangement has been replaced in Fig. 3 by a tap 30 of the transformer secondary winding 21, through a conductor III, diode anodes I09 and I09, cathode I0'I, resistor 40, and resistor 90 and condenser 96 in parallel to terminal 29 of trans- The input circuit of the triode, which functions as both detector and amplifler in this modification, is the same as that for detector 39 in the circuit of Fig. 2, except that the potential diflerence across resistor 45,

caused by current flow in the rectifier circuit,v

is utilized to bias control electrode I06 negatively with respect to cathode I01. This bias potential is applied through resistor 52, and operates to maintain the triode nonconductive ex- 00 cept when a fluctuating potential is superimposed upon it or in other words a flame exists between electrode 49 and ground.

' Fig. 6 illustrates a modification of the circuit of Fig. 5, in which the position of the resistor 90 p Voltage when t mode 1 is positiv so and the condenser 30 has been changed from the that amplifler 9| will be non-conductive in the absence of an impulse supplied through condenser I00, which condenser serves to isolate control electrode 04 from constant potentials existing in the detector circuit. The normal grid-biasing voltage is therefore supplied independently of the detector circuit in this modification, and in case of failure of the detector, the amplifier output would be cut 01!, thus causing the system to cease operation. This is a particcathode side of the rectifier to the anode side,

and which may be more desirable than the circult of Fig. 5 for some types of electronic tubes.

It will be readily understood by those skilled in 7 the art that the relayarrangements of Figs..1

and 2 are interchangeable, and that either one *may be used in any of the circuits shown.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of my invention now known to me, it will be apparent to those skilled that changes may be made-in the form of the app ratus disclosed without departing from the spirit of my--invention as set forth in the appended claims, and that in some cases certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A combined safety and quality control system for a fuel burner including fuel and air supply means, igniting means to establish a flame at said burner, a device to control said fuel supply means, and means to control the mixture of fuel and air supplied to said burner comprising in combination, a pair of spaced electrodes insulated from each other and positioned in the path of said flame. and means connected to said electrodes and responsive to the conductance of the path therebetween to control said control device and said mixture control means.

2. A combined safety and quality control system for a fuel burner including fuel and air supply means, igniting means to establish a flame at said burner, a device to control said fuel supply means, and means to control the mixture of fuel and air supplied to said burner comprising in combination, a pair of spaced electrodes insulated from each other and positioned in the path of said flame, a device to operate said fuel supply control device, a device to operate said mixture control means, and means connected to said electrodes and responsive to the conductance of the path therebetween to control said operati s devices.

3. A combined safety and quality control system for a fuel burner including fuel and air supply means, igniting means to establish a flame at said burner, a device to control said fuel supply means, a valve to control the mixture of fuel and air supplied to said burner, and a device to operate said valve comprisin in combination, a pair of spaced electrodes insulated from each other and positioned in the path of said flame, a current responsive device to operate said flrst mentioned device, a current responsive device to operate said second mentioned device and having an operating characteristic such that when energised with current of'a predetermined range it actuates said second mentioned device to open said valve and when energized with current of a diiferent predetermined range it actuates said second mentioned means to close said valve, and means adapted to be connected to am of electrical energy and to said electrodes and responsive to the conductance of the path between 7 said electrodes to control the energization of said current responsive devices.

4. A combined safety and quality control system for a fuel burner including fuel and air supply means, igniting means to establish a flame at said burner, a device to control said means having two operating conditionsone permitting and the second preventing establishment of a flameat the burner, and means to control the mittureof fuel and air supplied to said burner comprising in combination, a pair of spaced electrodes insulated from each other and positioned inthe path of said flame, a current responsive device to operate said control device and adapted when energised to actuate said control device to its flrst mentioned operating condition and adapted when deenergiaed to actuate said control device to its second mentioned operating condition, a current responsive device to operate said mixture control means, and means adapted to be connected to a source of electrical energy and to said electrodes and responsive to the conductance of the path between said electrodes to control said current responsive devices.

5. A safety control system for a fuel burner including means to establish a flame at said burner and a device to control said means comprising in combination, a pair of spaced electrodes insulated from each other and positioned in the path ofsaid flame, a device fo operating said control device, a circuit adapted to connect said operating device to a source of electrical energy, and means to control the conductivity of said circuit in response to fluctuations in the conduct.- annce between said electrodes, said last mentioned means being insensitive to steady values of conductance between said electrodes.

6. A safety control system for a fuel burner including means to establish a flame at said burner, and a device to control said means com; prising in combination, a pair of spaced eke-'- trodes insulated from each other and positioned in the path of said flame, a current responsive device for operating said control device and adapted when energized to actuate said control device to permit the establishment of a flame at said burner and adapted when deenergized to actuate said control device to prevent the establishment of a flame at said burner, means adapted to connect said current responsive deivice to a source of electrical energy including .an electric discharge device having an input circuit and an output circuit in .which said current re. sponsive device is connected, and means to control the input circuit of said discharge device in response to fluctuations in the conductance between said electrodes, said last mentioned means being insensitive to steady values of conductance between said electrodes.

'7. A safety control system for a fuel burner including means to establish a flame at said burner. and a device to control said means comprising in combination, a pair of spaced electrodes insulated from each other and positioned in the path of said flame, a current responsive device for operating said control device and adapted when energized'to actuate said control device to permit the establishment of aflame at said burner and adapted when deenergized'to actuate said control device to prevent the estab lishment of a flame at said burner, means adaptied to connect said current responsive device to a source of electrical energy including an electric discharge device having an input circuit and an output circuit in which said current responsive device is connected, and a connection between said electrodes and input circuit of said discharge device including a reactance to control said input circuit in response to fluctuations in the conductance between said electrodes, said last mentionedconnection being insensitive to steady values of conductance between said electrodes. v r

8. A combustion quality control system for a fuel burner including fuel and air supply means, igniting means to establish a flame at said burner, and a device to control the mixture of fuel and air supplied tosaid burner comprising in combination, a pair of spaced electrodes insulated from eachother and positioned in the path of said a device for operating said control device,-1a circuit adapted to connect said second mentioned device to a source of electrical energy, and an electric discharge device having an output circuit connected in said first mentioned circuit and an input circuit controlled by fluctuations in amplitude of the conductance between said electrodes but insensitive to steady values of said conductance.

9. A combustion quality control system for a fuel burner including fuel and air supply means, igniting means to establish a flame at said burner, a valve to control the mixture of fuel and air supplied to said burner, and a device to operate said valve comprising in combination, a pair of spaced electrodes insulated from each other and positioned in the path of said burner fiame, a current responsive device to operate said first mentioned device and having an operating characteristic such that when energized with current of a predetermined range it actuates said first mentioned device to open said valve, when energized with current of a second and difierent predetermined range it actuates said first mentioned device to maintain said valve stationary, and when energized with current of a third and different predetermined range it actuates said first mentioned device to close said valve, a circuit adapted to connect said current responsive device to a source of electrical energy, and an electric discharge device having an output circuit connected in said first mentioned circuit and an input circuit controlled by fluctuations in amplitude of the conductance between said electrodes but insensitive to steady values of said conductance.

10. In combination, fuel burner means to produce a conductance having the characteristic of normally fluctuating in magnitude, means in contact with said conductance at displaced positions and constituting terminals thereof, a device operable in one sense indicating the presence of fluctuations in magnitude of said cnductance and one condition of, operation of said burner and operable in another sense indicating the absence of fluctuations in magnitude of said conductance and another condition of operation of said burner, a source of electrical energy, an electric circuit for operating said device in said one sense in response to the presence of fluctuations in the magnitude of said conductance including an-electric discharge device having an input circuit and an output circuit, a connection between said output circuit and said first mentioned device including said source of energy, and means including a connection to said conductance through said terminals to control the input circuit of said discharge device in response to the presence of fluctuations in the magnitude of said conductance.

11. In combination, fuel burner means to produce a conductance having the characteristic of normally fluctuating in magnitude, means in contact with said conductance at displaced positions and constituting terminals thereof, a device operable in one sense indicating the presence of fluctuations in magnitude of said conductance and one condition of operation of said burner and operable in another sense indicating the absence of fluctuations in magnitude of said conductance and another condition of operation of said burner, a source of electrical energy, an electric circuit for operating said device in said one sense in response to the presence of fluctuations in the magnitude of said conductance including an electric discharge device having an input circuit and an output circuit, a connection between .said output circuit and said flrst'men tioned device including said source of energy, a reactance, and means including said reactance and a connection to said conductance through said terminals to control the input circuit of said discharge device in response to the presence of fluctuations in the magnitude of said conductance.

12. In combination, fuel burner means to produce a conductance having the characteristic of normally fluctuating in magnitude, means in contact with said conductance at displaced positions and constituting terminals thereof, a, device operable in one sense indicating 'the presence of fluctuations in magnitude of. said conductance and one condition of operation of said burner and operable in another sense indicating the absence of fluctuations in magnitude of said conductance, and another condition of operation of said burner, a source of electrical energy, an electric circuit for operating said device in said one sense in response to the presence of fluctuations in the magnitude of said conductance including an electric discharge device having an input circuit and an output circuit, a connection between said output circuit and said first mentioned device including said source of energy, a second electric discharge device having an input circuit and an output circuit, a connection between the output circuit of said second mentioned discharge device and the input circuit of said first mentioned discharge device including said source of energy and means including a connection to said conductance through said terminals to control the input circuit of said second mentioned discharge device in response to the presence of fluctuations in the magnitude of said conductance.

13. In combination, fuel burner means to produce a conductance having the characteristic of normally fluctuating in magnitude, means in contact with said conductance at displaced positions and constituting terminals thereof, a device operable in one sense indicating the presence of fluctuations in magnitude of said conductance and one condition of operation of said burner andoperablein anothersense indicating the absence of fluctuations in magnitude of said conductance and another condition of operation of said burner, a source of electrical energy, an electric circuit for operating said device in said one sense in response to the presence of fluctuations in the magnitude of said conductance including an electric discharge device having an input circuit and an output circuit, a connection between said output circuit and said first mentioned device including said source of energy, a second electric discharge device having an input circuit and an output circuit, a connection between the output circuit of said second mentioned discharge device and the input circuit of said first mentioned discharge device including said source of energy, a reactance and a, connection to said conductance through said terminals, and means including said reactance to control the input circuit of said second mentioned discharge device in response to the presence of fluctuations in the ductance.

14. In combination, fuel burner means to produce a conductance having the characteristic of normally fluctuating in magnitude, means in contact with said conductance at displaced positions and constituting terminals thereof, a device operable in one sense indicating the presence magnitude of said con-- of fluctuations in magnitude of said conductance and one condition of operation of said burner and operable in another sense indicating the absence of fluctuations in magnitude of said conductance and another condition of operation of said burner, a source of electrical energy an electric circuit for operating said device in said one sense in response to the presence of fluctuations in the magnitude of said conductance including an electric discharge device having an input circuit and an output circuit. a connnection between said output circuit and said first mentioned device including said source of energy, a second electric discharge device having an input circuit and an output circuit, a reactance, a connection between the output circuit of said second mentioned discharge device and the input circuit of said first mentioned discharge device including said reactance and said source of energy, and means including a connection to said 'conductance through said terminals to control the input circuit of said second mentioned discharge device in response to the presence of fluctuations in the magnitude of said conductance.

15. In combination, fuel burner means to produce a conductance having the characteristic of normally fluctuating in magnitude, means in contact with said conductance at displaced positions and constituting terminals thereof, a device operable in one sense indicating the presence of fluctuations in magnitude of said conductance and one condition of operation of said burner and operable in another sense indicating the absence'of fluctuations in magnitude of said conductance and another condition of operation of said burner, a source of electrical energy. an electric circuit for operating said device in said one sense in response to the presence of fluctuations in the magnitude of said conductance including an electric discharge device having an input circuit and an output circuit, a connection between said output circuit and said first mentioned device including said source of energy, a second electric discharge device having an input circuit and an output circuit, a reactance, a connection between the output circuit of said second mentioned discharge device and the input circuit of said flrst mentioned discharge device including said reactance and said source of energy, a second reactance, and means including said second reactance and a connection to said conductance through said terminals to control the input circuit of said second mentioned dis- "charge device in response to the presence of fluctuations in the magnitude of said conductance.

16. In combination, fuel burner means to produce a varying conductance, means in contact with said conductance at displaced positions and constituting terminals thereof, a device adapted to be positioned in accordance with the amplitude of variation of said conductance to determine the condition of operation of said burner means, a source of electrical energy, an impedance, an electric discharge device having an input circuit and an output circuit, a connection between said output circuit and said device including said source of energy, a connection between said impedance and said input circuit, and means including a connection to said conductance through said terminals for producing a varying potential across said impedance substantially in proportion to the variations of said conductance.

17. In combination, fuel burner means to produce a varying conductance, means in contact with said conductance at displaced positions and constituting terminals thereof, a device adapted to be positioned in accordance with the amplitude of variation of said conductance to determine the condition of operation of said burner means, a source of electrical energy, an impedance, an electric discharge device having an input circuit and an output circuit, a connection between said output circuit and said device including said source of energy. a connection between said impedance and said input circuit, and means including a reactance and a connection to said conductance through said terminals for producing a varying potential across said impedance substantially in proportion to the variations of said conductance.

18. In combination, fuel burner means to produce a varying conductance, means in contact with said conductance at displaced positions and constituting terminals thereof, a device adapted to be positioned in accordance with the amplitude of variation of said conductance to determine the condition of operation of said burner means, a source of electrical energy, an electric discharge device having an input circuit and an output circuit, a connection between said output circuit and said device including said source of energy, a second electric discharge device having an input circuit and an output circuit, a connection between the output circuit of said second mentioned discharge device and the input circuit of said flrst mentioned discharge device including said source of energy, and means connected to the input circuit of said second mentioned discharge device and including a connection to said conductance through said terminals to control the conductivity of said second mentioned discharge device substantially in proportion to the variations of said conductance.

19. In combination, fuel burner means to produce a varying conductance, means in contact with said conductance at displaced positions and constituting terminals thereof, a device adapted to be positioned in accordance with a the amplitude of variation of said conductance to determine the condition of operation of said burner means, a source of electrical energy, an electric discharge device having an input cir-v cuit and an output circuit, a connection between said output circuit and said device including said source of energy, a second electric discharge device having an input circuit and an output circuit, a connection between the output circuit of said second mentioned discharge device and the input circuit of said flrst mentioned discharge device including said source of energy, a reactance and a connection to said conductance through said terminals, and means including said reactance and connected to the input circuit of said second mentioned discharge device to control the conductivity of said second mentioned discharge device substantially in proportion to the variations of said conductance.

20. In combination, fuel burner means to produce a varying conductance, means in contact with said conductance at displaced positions and constituting terminals thereof, a device adapted to be positioned in accordance with the amplitude of variation of said conductance to determine the condition of operation of said burner means, a source of electrical energy, an electric discharge device having an input circuit and an output circuit, a connection between said output circuit and said device including said source of energy, a'second electric discharge device having an input circuit and an output circuit, a reactance, a connection between the output circuit of said second mentioned discharge device and the input circult of said flrst mentioned discharge device including said reactance and said source of energy, and means connected to the input circuit of said second mentioned discharge device and including a connection to said conductance through said terminals to control the conductivity of said second mentioned discharge device substantially in proportion to the variations of said conductance.

21. In combination, fuel burner means to produce a varying conductance. means in contact with said conductance at displaced positions and constituting terminals thereof, a device adapted to be positioned in accordance with the amplitude of variation of said conductance to determine the condition of operation of said burner means, a source of electrical energy, an electric discharge device having an input circult and an output circuit, a connection between said output circuit and said device including said source of energy, a second electric discharge device having an input circuit and an output circult, a reactance, a connection between the output circuit of said second mentioned discharge device and the input circuit of said first men tioned discharge device including said reactance and said source of energy, a second reactance, and means including said second reactance and a connection to said conductance through said terminals and connected to the input circuit of said second mentioned discharge device to control the conductivity of said second mentioned discharge device substantially in proportion to the variations of said conductance.

22. A safety control system for a fuel burner including means to establish a flame at said burner, and a device to control said means comprising in combination, a pair of spaced electrodes insulated from each other and positioned in the path of said flame, a device for operating said control device, a circuit adapted to connect said operating device to a source of electrical energy, and means to control the conductivity of said circuit in response to fluctuations in the conductance between said electrodes to maintain said first mentioned means in flame producing condition.

23. A safety controlsystem for a fuel burner including means to establish a flame at said burner, and a device to control said means comprising in combination, a pair of spaced electrodes insulated from each other and positioned in the path of said flame, and means responsive the conductance between said condition.

24. A combined safety and quality control system for a fuel burner including fuel and air 25. A combined safety and quality control system for a fuel burner including fuel and air supply means and igniting means to establish a flame at said burner comprising in combination, a device to control said fuel supply means, means to control the mixture of fuel and air supplied to said burner, and means responsive to a characteristicof said flame indicative of flame presence and combustion quality to control said control device and said mixture control means.

26. A safety system for a fuel burner including means to establish a, flame at said burner comprising in combination, a device to control said means, and means responsive only to sustained fluctuations in a characteristic of said flame indicative of flame presence to control said device to maintain said first mentioned means in a flame producing condition.

27. A safety system for a fuel burner including means to establish a flameat said burner, and means responsive only to sustained fluctuations in a characteristic of said flame indicative of flame resence to control said flame establishing means.

28. A. safety system for a fuel burner including means to establish at said burner a flame having a fluctuating characteristic indicative of flame presence, and means responsive only to sustained fluctuations in said characteristic and including a device exposed to the region normally including said flame to operate said systern to control said flame establishing means and thereby the presence of a flame at said burner. K

2.9. A combustion control system for a fuel burner including means for producing combustion to establish a flame at said burner, and

means responsive only to sustained fluctuations in a characteristic of said flame indicative of normal combustion to control said combustion producing means.

30. A combustion control burner including means for producing combustion to establish a flame at said burner, comprising in combination, a pair of spaced electrodes insulated from each other and positioned in the path of said flame, and means connected to said electrodes and responsive to sustained fluctuations in the conductivity of said flame but insensitive to steady values thereof to control said combustion producing means.

31 Apparatus comprising a burner, means for supplying the elements of combustion to the burner, and means responding to the ratio between the elements of combustion supplied the burner comprising means responsive to changes in the amplitude of fluctuation in the electrical conductivity of the flame issuing from the burner and produced by the burning of the elements of combustion.

32. Apparatus comprising .a burner, means for supplying fuel and air to the burner, and means responding to the ratio between the fuel and air supplied the burner comprising a pair of spaced electrodes disposed to be enveloped in the flame issuing from said burner, an electric circuit including said electrodes, and means responding to changes in the amplitude of flucsystem for a fuel tuation in the conductivity of said circuit.

. 33. Apparatus comprising a burner, means for supplying fuel and oxygen to the burner, and means responding to the ratio between the fuel and oxygen supplied to the burner comprising an electric circuit including a portion of the flame produced by the burning of the fuel and oxygen, and means responding to changes in the amplitude of fluctuation in the electrical conductivity of said circuit.

34. Apparatus comprising a burner, means for supplying the elements of combustion to the burner, and means responding to the ratio between the elements of combustion comprising an electric circuit including a portion of the flame produced by the burning or the elements 01 combustion, and means responding to changes in the amplitude 01' fluctuation in the electrical conductivity of said circuit.

35. In combination, a furnace, means for supplying the furnace with the elements of combustion, means responding to changes in the amplitude of fluctuation in the electrical conductivity of the flame produced by the combustion of the elements of combustion, and means for controlling the ratio betweenthe elements of combustion supplied the furnace in correspondence with the changes in amplitude of. fluctuation in the electrical conductivity of the flame.

36. The method of maintaining a desired fuelair ratio to a i'urnace which includes increasing and decreasing the fuel-air ratio in correspondence'with the decreases and increases. respectively. in the amplitude of fluctuation in the electrical conductivity of the flame produced by burning of the fuel and air.

37. The method of obtaining response to the ratio between the elements of combustion supplied a flame which includes obtaining response to changes in the amplitude of fluctuation in the electrical conductivity of the flame resulting from the combustion of the elements.

38. The method of obtaining response to the completeness of combustion which includes obtaining response to changes in the amplitude of fluctuation in the electrical conductivity of the flame produced by such combustion;

WALTER P. WILLS. 

